If I'm not mistaken, this is an HTML question rather than PHP (it could be database, though). The answer is the same, however: the same way you would any other page. The index file is no different from any other HTML/PHP file.
To adjust a table, just add width="width" and height="height" somewhere in the table, row or cell:
<table width="100%" height="50%">
<tr height="50%">
<td width="100%">cell</td>
</tr>
<tr height="50%">
<td>cell2</td>
</tr>
</table>
To add a new table, just add the same code you had before.